tum
of rock is labelled by its fossil population; and that the order of
succession of such groups of fossils is always the same in any vertical
series of strata in which they occur. That is to say, if fossil A
underlies fossil B in any given region, it never overlies it in any
other series; though a kind of fossils found in one set of strata may
be quite omitted in another. Moreover, a fossil once having disappeared
never reappears in any later stratum.

From these novel facts Smith drew the commonsense inference that the
earth had had successive populations of creatures, each of which in
its turn had become extinct. He partially verified this inference by
comparing the fossil shells with existing species of similar orders,
and found that such as occur in older strata of the rocks had no
counterparts among living species. But, on the whole, being eminently
a practical man, Smith troubled himself but little about the inferences
that might be drawn from his facts. He was chiefly concerned in using
the key he had discovered as an aid to the construction of the first
geological map of England ever attempted, and he left to others the
untangling of any snarls of thought that might seem to arise from his
discovery of the succession of varying forms of life on the globe.

He disseminated his views far and wide, however, in the course of his
journeyings--quite disregarding the fact that peripatetics went out of
fashion when the printing-press came in--and by the beginning of the
nineteenth century he had begun to have a following among the geologists
of England. It must not for a moment be supposed, however, that his
contention regarding the succession of strata met with immediate or
general acceptance. On the contrary, it was most bitterly antagonized.
For a long generation after the discovery was made, the generality of
men, prone as always to strain at gnats and swallow camels, preferred to
believe that the fossils, instead of being deposited in successive ages,
had been swept all at once into their present positions by the current
of a mighty flood--and that flood, needless to say, the Noachian deluge.
Just how the numberless successive strata could have been laid down
in orderly sequence to the depth of several miles in one such fell
cataclysm was indeed puzzling, especially after it came to be admitted
that the heaviest fossils were not found always at the bottom; but to
doubt that this had been done in some way was rank